Preparation of monocarboxylic acids



Patented Nov. 27, 1934 UNITED STATES PREPARATION OF MONOCARBOXYLIC I ACIDS Johannes Brode and Adolf Johannsen, Ludwigshafen-on-the-Rhine, Mannheim,

Germany,

assignors to I. G. Farbenindustrie Aktiengesellschaft, Frankfort-on-the-Main, Germany, a corporation of Germany No Drawing. Application April 21, 1928, Serial 9 Claims.

The present invention relates to the production of monocarboxylic acids from dicarboxylic acids or their anhydrides.

, This application is a continuation in part of our application Ser. No. 149,520, filed November 19, 1926, now Patent No. 1,955,050, dated April 17, 1934, in which application we have described and claimed a process for the manufacture of monocarboxylic acids from dicarboxylic acids 10 with the aid of catalysts capable of splitting ofi carbon dioxid. In the said process dicarboxylic acids or their anhydrides, the latter together with water vapor which, however, is preferably also added when starting from dicarboxylic acids, are passed, alone or together with other gases over the aforesaid catalysts at temperatures between about 250 and 500 0., preferably between 300 and 450 C. As stated in the aforesaid application Ser. No. 149,520, lead oxid is a particular valuable catalyst, whether employed alone or in conjunction with other compounds, such for example as oxids of other metals and the like.

The reaction is advantageously carried out with an excess of Water vapor over the quantity theoretically required; however, the process may also be carried out by exposing the vapor mixture formed by heating dicarboxylic acids (which mixture consists probably of the dicarboxylic acid, its anhydride and water vapor) directly over the catalyst. When starting from dicarboxylic acid anhydrides, an addition of water vapor to the anhydride vapor is necessary, as stated above.

The operation with a gas or air current containing water vapor ofiers often advantages over the use of water vapor alone, as, for example, in the conversion of phthalic anhydride into benzoic acid, the concentration of the water vapor and the temperature at which the separation of the reaction products takes place, may be so chosen 40 as to obtain the reaction product directly in a solid, practically dry form; this results in the purification and further use of the reaction product being much facilitated.

The dicarboxylic acid anhydrides employed as initial materials in the process above mentioned, for example phthalic anhydride, maleic anhydride and the like, may be obtained by the catalytic oxidation of vapors of hydrocarbons or their derivatives such as naphthalene, naphthol, benzene, phenol and the like.

We have further found that when the dicarboxylic acid anhydrides are prepared by catalytic reactions in the vapor phase, such for example as have been mentioned before, it is not necessary to separate the anhydride from the re- In Germany November 27, 1925 action mixture, but the latter may be passed di-' rectly or after an addition of water vapor has been made, over the catalyst comprising lead oxid. This method of working is of particular advantage when the anhydrides are prepared by the catalytic oxidation of hydrocarbons or derivatives thereof.

The following example will further illustrate the nature of this invention which, however, is not limited to this example.

Example A gaseous mixture containing per cubic meter air 33 grams of phthalic anhydride vapor and about 45 grams of water vapor is passed at 350 to 360 C..over a catalyst comprising lead oxid precipitated on to a support of pumice. The said catalyst is advantageously prepared by spraying a solution of lead nitrate on heated pumice and heating the product in a current of air to between 350 and 400 C. On cooling the gaseous reaction mixture the bulk of the benzoic acid formed separates as a dry, white product of more than 99 per cent purity. The yield in benzcic v acid amounts to about 90 per cent of the theoretical yield calculated on the amount of phthalic anhydride used.

Instead of lead oxid alone also mixtures thereof with other oxids such as alumina or zinc oxid or with silicates such as kaolin may be used. When 5 using air as a carrying gas, such oxids should be chosen as additions as do not exert an oxidizing action on the benzoic acid formed at the temperature of the reaction.

What We claim is:

1. The process of producing monocarboxylic acids which comprises passing the vapors of a dicarboxylic acid at between about 250 and about 500 C. over a catalyst essentially comprising lead oxid.

2. The process of producing monocarboxylic acids which comprises passing the vapors of a dicarboxylic acid together with water vapor at between about 250 and about 500 C. over a catalyst essentially comprising lead oxid.

3. The process of producing monocarboxylic acids which comprises passing the vapors of a dicarboxylic acid anhydride together with water vapor at between about 250 and about 500 C. over a catalyst essentially comprising lead oxid. 105

4. The process of producing monocarboxylic acids which comprises passing the vapors of a dicarboxylic acid anhydride together with water vapor at between about 300 and about 450 C. over a catalyst essentially comprising lead oxid.

5. The process of producing benzoic acid which comprises passing phthalic anhydride vapor together with water vaporat between about 250 and about 500 C. over a catalyst essentially comprising lead oxid.

6. The process of producing benzoic acid which comprises passing phthalic anhydride vapor together with water vapor and an oxygen containing gas over a catalyst essentially comprising lead oxid and another metal oxid not activatingoxygen at between about 300 and about 400 C.

'7. The process of producing benzoicacid which comprises passing phthalic anhydride vapor together with water vapor over lea'doxid'at between about 330 and about 380 C. I

comprising lead oxid.

8. The process of producing monocarboxylic acids which comprises passing the gas mixture resulting from the catalytic manufacture of a dicarboxylic anhydride in the vapor phase at between about 250 and. about 500 C. over a catalyst essentially comprising lead oxid.

9. The process of producing benzoic acid which comprises subjecting naphthalene vapor to eatalytic oxidationsto phthalic anhydride and passing the resulting gas mixture at between about 250 and about 500 C. over a catalyst essentially J OHANNES BRODE. ADOLF J OHANNSEN. 

